1. My name is Margaret and have always gone by Maggie. My mother never had any trouble getting people to agree to the nickname. Maggie is a traditional nickname for Margaret though so it's not exactly the same as your situation, but they still are 2 quite different names.

2. My sister's name is Stephanie and my mother decided before she was born that she was going to be called Stevie (a-la Stevie Nicks, it was all very 80s you see). She was probably called Stevie a total of 3 times right after she was born and that was the end of that.

Anyway I think you'd have to be persistent, but its definitely doable. Just introduce him as Huck, then if people ask for the full name after that, Huck will probably still be seen as the primary name.

one maybe - if you contort their variations and back stories enough. which i dont think is the point of a nickname.

i think people wish they could use these 'forced' nicknames as real names but they are just too scared.

in this last ladys case it would have been fine, they werent too 'nicknamey' and could easily stand alone as a first name.

in your case Huck is the nickname for Huckleberry, done. its the reason people name their kid Huckleberry in the first place. and since Huck is so charming on his own and thats all he will ever be called his entire life, why not cut down on paperwork and trouble and just name him Huck?

I have limited experience, but here is mine so far, we named our son Theodore last year with the intention of calling him Theo most of the time. So far we do, with the occasional full Theodore thrown in there and EVERYONE calls him Theo. We have not had one person try to call him anything else. If I introduce him as Theodore, I do get "Teddy?" occasionally, and I simply respond with "We call him Theo".. Huck is the intuitive nickname for Huckleberry so I think people will take to it easily.

If I met a Henry nicknamed Huck, after hearing the parents say it a few times I'm sure Huck would just feel like his name, simple as that

This, exactly. My sister's name is Elizabeth nn Betsy. While I know that was a popular nn for a while, it was pretty past its prime when she was named (she's 24 now). But regardless, I never remember anyone trying to call her Beth or Liz or something, because her name is Betsy and it would be weird to call her anything else.

A few stories:
My friend Rebecc@ introduces herself as Rebecc@. Within five minutes she's Becc@. Sometimes it's really natural on a person.
My fried P@vneet has been P@vi for as long as I've known her. Even though we all know that she's 'really' P@vneet, no one really knows who that is without thinking for a second.
My little sister Aish@ is named after our grandmother. Before she was even born, our aunt remarked that she could be called U$hie (like pushy). Now she's U$hie about 80% of the time at home or with family friends/my close friends. Her school friends know her as Aish@, but they do sometimes switch when they come here and hear us calling her U$hie!
(Masking for Google purposes)